In a conventional apparatus for preparing ice creams, e.g. as described in U.S. Pat. No. 4,703,628, both the freezing cylinder and ice creams are sterilized while a high-temperature refrigerant gas is circulating through the freezing cylinder, and the ice creams are being kept in the inside of the cylinder In this case, there is a problem in that when a high thermal death point is preset to obtain an excellent sterilization effect, such kind of ices as an ice cream will generate a smell of something burnt, and the flavor of the ice creams reproduced from such ices will be greatly injured.
For the avoidance of such problems, a system is also known as shown in Japanese Patent Early Publication No. 54-37223 for example. In this system, the freezing cylinder is sterilized by boiling water after collecting ice creams in the cylinder. However, in the system described in the above publication, city water is heated in the tank in which the temperature and the quantity of the contents of it are controlled, a prescribed quantity of the boiling water is supplied to the material tank and the freezing cylinder when cleaning and sterilization are needed, and the used boiling water is discharged by opening the gate plunger of the product dispenser after a prescribed period of time controlled automatically. Hence this conventional system has drawbacks in that since the boiling water heated in advance in the tank is fed to the material tank and the freezing cylinder, a large quantity of heat is lost through conduction and radiation to the air in the cylinder, tank, and piping, the temperature of the fed boiling water falls below thermal death points, and satisfactory sterilization can hardly be expected.
Further, in this kind of ice cream manufacturing apparatus, as seen in U.S. Pat. No. 4,703,628, there was only one freezing cylinder to stir and refrigerate ice-cream materials. A plural kinds of flavor piping are connected to such one cylinder such that one of flavors was selected and mixed with the ice creams obtained from the freezing cylinder, and the finished ice creams were poured into a container.
However, such a one-cylinder apparatus caused problems in that since there was only one cylinder, the dispensing of ice creams could not overtake a great demand in summer, and when there was a mechanical trouble no sales were possible.
Accordingly, a two-cylinder apparatus is considered favorable. However, it also caused problems in that a small demand in winter made the products remain unsold, and they had to be wastefully thrown away every day.
By the way, this kind of ices has a luscious taste peculiar to milk fats, and this lusciousness can be softened to some extent by enlarging ice crystals contained in ices.
So, as shown in Japanese Patent Early Publication No. 61-47,149, a liquid mix, a material for ices, has hitherto been entered the freezing cylinder, and once heated prior to refrigerating operations which have been carried out after pull-down operations. Large ice crystals have been formed such that the liquid mix which was hardened through the pull-down operation was thawed to be separated into fat and water through such a heating operation, and then the liquid mix in this separated state was refrigerated through usual refrigerating operations.
However, above-mentioned conventional technology had problems in that since a refrigerated liquid mix must once be heated so as to form large-particle ice crystals, it takes a lot of time to enter into such usual refrigerating operations.